[LARTC] ceil, cburst, prio not working?

[L Rotger]

Hi, I've been using htb fine to separate outgoing SMTP traffic from HTTP 
traffic so sending big emails doesn't affect browsing. As long as ceil 
== burst and the sum of all rates don't exceed the root class' rate all 
is fine but when I incorporate ceil I would expect (from lartc howto) 
that when other classes are idle the remaining bandwith would be 
assigned in order of prio (I believe, again from howto that 0 is 
highest) to other classes, which is not happening.

In particular, sending big test emails (with everything else idle) shows 
that SMTP traffic never exceeds exactly 3kbps, even with ceil set at 
9kbps. I measured the speed with iptraf. What am I doing wrong?

List of my classes. If you need more info, please let me know!

# tc class show dev eth2
class htb 1: root prio 0 rate 13312bit ceil 13312bit burst 1732b cburst 5Kb
class htb 1:20 root prio 7 rate 12bit ceil 12bit burst 1599b cburst 1599b
class htb 1:5 root prio 2 rate 13312bit ceil 13312bit burst 1732b cburst 
1732b
class htb 1:6 root prio 3 rate 13312bit ceil 13312bit burst 1732b cburst 
1732b
class htb 1:7 root prio 4 rate 4096bit ceil 4096bit burst 1639b cburst 5Kb
class htb 1:8 root prio 5 rate 3072bit ceil 9216bit burst 1629b cburst 
1691b
class htb 1:9 root prio 6 rate 3072bit ceil 9216bit burst 1629b cburst 
1691b

root class: 1:0
siblings: 1:5, 1:6, 1:7, 1:8, 1:9, 1:20
SMTP outgoing traffic goes out 1:8

1:20 is the default so all non-specifically filtered traffic goes out 
slowly (rate is 0.1kbit) so I know what's left to filter.

Thanks in advance!
L Rotger